1. Technical Field of the Invention
This invention relates to an apparatus for producing a flat tube, in which a material to be worked into a desired shape is gradually formed so as to eliminate defective forming, such as buckling and the like of the material being worked, and in particular, for producing a tube through which a fluid flows to exchange heat in a heat exchanger, such as a vehicle radiator and a hot water-type heating apparatus. The invention, further, relates to a method of producing the flat tube.
2. Description of the Related Art
A pipe-forming method has heretofore been known for forming a thin sheet metal material into a pipe based on a plastic working method. As the pipe-forming method, it is a generally accepted to employ a continuous roll forming process as described below from the standpoint of productivity.
For instance, JP-A-10-272513 discloses a method of producing a pipe by using a pipe producing apparatus, wherein a band-like material having high spring-back characteristics is deformed into the shape of a pipe, the deformed pipe is wound in the form of a flat plate and is easily unwound to form a pipe.
JP-A-10-137842 discloses an apparatus for continuously producing a thin pipe, comprising a pre-bending roller, a subsequent pair of patches for executing the forming from a bent shape into a U-shape, and another subsequent pair of patches for executing the forming from the U-shape into a C-shape, which are arranged on both the right and left sides of the band-like blank so that the pre-bent band-like blank is gradually made from the U-shape into the C-shape in cross section as it passes through the right and left patches.
Further, JP-A-8-103818 discloses a method of continuously producing a tapered pipe by passing a blank coil between a plurality of pairs of pipe-forming rollers, wherein settings of the pipe-forming apparatus having the pipe-forming rollers are varied depending upon a change in the width of the blank coil that passes through the pipe-forming rollers.